Post no 2 presumably refer to US standards...
No "rules" in UK or EU that I am aware of.
Good practice dictates their use as appropriate. Seldom used above FL100, traditionally by consensus always used below FL100 in controlled airspace. Some operators using retractable lights (usually newer companies who tend to "know better" than the rest of the established industry) have recently developed a bizarre habit of turning them off - ie retracting them - apparently on a fuel-saving basis almost immediately after take off even in the most crowded airspace. This is apparently done on the basis of an assumed miniscule fuel saving (ie brownie points) instead of maintaining good visibility and conformity with everyone else, ie airmanshi...shi!...shi!!
Oh Bugger! I said it again!
I'll get my yellow roadmender's coat.
Last edited by Agaricus bisporus; 17th Dec 2012 at 21:20.